Combustion model evaluation in a CFD simulation of a radiant-tube burner

•A significant difference in the reaction zone is observed comparing the combustion models.•The skeletal kinetic mechanisms used with the EDC model adequately describe the evaluated system.•The burner geometry was responsible for the small difference in the RT temperature prediction between combustion models.•The 2-D axisymmetric simulation gives good results as compared with the 3-D simulation. This work presents the computational fluid dynamic (CFD) simulation of a single-ended non-recirculating radiant tube burner (RTB). In the RTB evaluated, the mixing and main combustion reactions take place inside a combustion chamber, which differs from most of the RTB configurations found in the literature. The eddy-dissipation-concept (EDC) model and the Steady-Diffusion-Flamelet (SDF) model were compared to contrast their performance in the studied burner. Five chemical kinetic mechanisms were evaluated with the two combustion models. The chemical equilibrium approach with a PDF tabulation was also included. The CFD simulations were made using an axisymmetric two-dimensional (2-D) computational domain. The performance of the CFD simulation was evaluated by comparing its predicted outer radiant tube (RT) temperature with experimental measurements. Temperature and mole fraction of CO and OH were also compared between models and kinetic mechanisms. A third model, the Flamelet Generated Manifold (FGM), was subsequently included in the analysis, due to its capability to describe partially premixed combustion. Finally, the results of the 2-D simulation were contrasted with a three-dimensional (3-D) simulation, determining the effect of geometry simplification and confirming the suitability of 2-D CFD models in the studied case.